1. Technical Field
The present invention generally relates to a method for fabricating an optical device and more particularly to a method for fabricating an optical device for improving the fabrication yield.
2. Description of the Related Art
With the continuous development and growth of electronic commodities such as cameras and scanners, the demand of image sensors is continuing to increase in the consumer market. Nowadays commonly used image sensors include charge coupled device (CCD) and CMOS image sensor (CIS). Since the CMOS image sensor has the advantages of low operating voltage, low power consumption, high operation efficiency and random access, it can be integrated with the current semiconductor technology for mass production, and therefore it is widely applied.
FIG. 1A and FIG. 1B are schematic cross-sectional views of a conventional CMOS image sensor illustrating process steps of a fabricating process. Referring to FIG. 1A, first, a dielectric layer 130, a filter array 150, a planarizing layer 160 and a micro-lens array 170 are sequentially formed over an element region 102 of a semiconductor substrate 100. The element region 102 of the semiconductor substrate 100 has a plurality of photosensitive elements 110 formed therein. A circuit pattern 120 and a bonding pad 140 electrically connected with the circuit pattern 120 are formed over a peripheral region 104 of the semiconductor substrate 100 has. The dielectric layer 130 has an opening 132 exposing the bonding pad 140.
Referring to FIG. 1B, a protective layer 180 is subsequently formed over the micro-lens array 170 for protecting the micro-lens array 170 from damage by particulates or other contamination sources. Since the protective layer 180 is also filled into the opening 132 and covers the bonding pad 140, an etching process is required to remove a portion of the protective layer 180 to expose the bonding pad 140 to facilitate the electrical connection of circuit pattern 120 with an external circuit in the subsequent process.
Generally speaking, the protective layer 180 is made of an inorganic material such as silicon oxide, silicon nitrogen or silicon oxynitride, and a dry etching using a fluorine-containing gas is performed to remove the portion of the protective layer 180 to expose the bonding pad 140. However, during the dry etching process, the fluorine-containing gas residues may adhere on the bonding pad 140, corrode the bonding pad 140, and result in the formation of indent or unevenness on the surface of the boning pad 140 leading to poor electrical connection between the bonding pad 140 and other element. Accordingly, it is necessary to use a cleaning process to remove the fluorine-containing gas residues on the bonding pad 140.
However, current chemical solvents used in the cleaning process for removing the fluorine-containing gas residues would cause peeling of the photo-resist material in the filter array 150, the planarizing layer 160 and the micro-lens array 170. Therefore, how to effectively remove the residual fluorine-containing gas residues on the bonding pad 140 without adversely influencing other elements or layers of the device is presently one of urgent issues that need to be resolved in the fabrication process of the CMOS image sensor.
Additionally, during the fabrication of conventional liquid crystal on silicon (LCOS) display panel, the above-mentioned issue is also encountered.